Stagger back, giving unpleasant look (4)
I believe the answer is:
'unpleasant look' is the definition.
(I've seen this before)
'stagger back' is the wordplay.
'stagger' becomes 'reel' (both can mean to move around without balance).
'back' is a reversal indicator.
'reel' back-to-front is 'LEER'.
'giving' acts as a link.
(Other definitions for leer that I've seen before include "Give sly look" , "Suggestive or sneering look" , "Stare suggestively" , "Suggestive or sneering grin" , "Lecherous look" .)